Patent GB-675760-A (GB)
Abstract: 675,760. Automatic control systems for aircraft. BENDIX AVIATION CORPORATION. Sept. 10, 1948 [Oct. 17, 1947], No. 23871/48. Class 38 (iv). In an approach control system for aircraft designed to operate with known localizer and glide flight path transmitters located at an airport and wherein receivers 10, 11 on the aircraft develop D.C. potentials proportional to the angular displacement of the aircraft from the localizer and glide beams respectively, provision is made for the derivation of control signals proportional to the angular displacement of the aircraft from the beam as well as the signals in known systems which are dependent only on the direction and length of time of displacement from the beam. To avoid dangerous response of the aircraft on sudden changes of beam direction if when the aircraft is taxiing-in front of or passes over a transmitter, application of the " angular displacement " signals to the control gear is made gradual. As shown in Fig. 1, automatic control of the rudder 19 is effected by an inductor compass 22, a rate-ofturn gyro 23 and a follow-back device 24. The signals from the compass 22 induced in the rotor 28 of an inductive device 26, are fed through an amplifier 31 to a motor 33 which resets the rotor 28 and operates a transmitter 34 which in turn operates the rudder servomotor 45. The rate of turn signals from gyro 23 are fed in series with those from the transmitter 34, the combined signals being passed through an amplifier 37. Altitude control by the ailerons 20 and elevators 21 is effected by bank and pitch take-offs 49, 50 of a horizon gyro 48, and the corresponding control servomotors 55, 63, and follow-back controls 57, 65. Flight and guide-path computers 38, 69 are provided and are associated with the automatic pilot when the aircraft is brought on to the landing ratio beams, by a switch 72, Fig. 3 (not shown) which applies the signal in receiver 10 to the leads 81, 82, Fig. 2, of a magnetic amplifier 83 of the type described in Specification 647,961, [Group XXXIX]. When the aircraft departs from the localizer flight path beam, an A.C. potential is developed at the output of the magnetic amplifier having a magnitude proportional to the angular displacement from the beam and a polarity dependent on the direction of displacement. This A.C. signal controls a discriminator valve 116 which reaches saturation on very small displacements from the beam and then develops an output which is a function only of the duration of displacement. The output controls through two valves 133, 139 thermal time delay devices 144, 151 which are connected via Wheatstone bridges to the control grids of an amplifier 173. The arrangement is such that one or other of the valves 133, 134 become operative dependent upon the direction of deflection of the aircraft to determine the polarity of potentials applied to resistors 182, 187, each valve controlling the thermal devices 144, 151 to produce by unbalancing the bridges, adjustment of those potentials which by reason of the time delay devices are adapted to reach a steady state after thirty seconds and four minutes respectively. The resistors 182, 187 thus produce signals which are representative only of the direction of deflection of the aircraft and the time period the aircraft is displaced from the localizer beam. A signal proportional to the angular displacement of the aircraft from the localizer beam is introduced into the circuit of the resistors 182, 187 by a resistor 232 connected to the output of a second magnetic amplifier 188 associated with the output of the receiver 10. To prevent dangerous response of the aircraft when the automatic approach system is connected up some distance from the axis of the localizer beam and the potentials across 232 tend normally to be large, provision is made for this signal to be applied gradually by limited amounts. This is effected by ensuring a slow build-up of the primary A.C. excitation of magnetic amplifier 188 by the provision of a thermal delay device 205 in the A.C. supply circuit, which device is brought into action by thermal and electromagnetic relays 206 ... 209 when the switch 72, Fig. 3 (not shown), is operated. When this switch is operated, the compass displacement signals are applied to leads 233, 234, Fig. 2, and thus the compass signal and the signals developed across resistors 182, 187, 232 are applied to the grids of a valve 249, the anode 252 of which is connected to resistor 258 in the rudder control channel while anode 253 is associated with the aileron channel 263 in similar manner. In order to compensate for the slow decay of potentials developed by the thermal delay devices 144, 151 and thus ensure that the computor signals are zero when the aircraft intercepts the beam, a feed-back signal for the magnetic amplifier 83 is derived from an amplifier valve 280. Reduced potentials may be derived from the rudder and aileron control resistors 258, 263 for " range " flying. A " safety " circuit controlled by a valve 289 is also provided, the arrangement being such that the development of excessive rudder and aileron control signals cancel releases of a relay 218 to short-circuit the signal sources. To fly along the vertical glide path the switch 72, Fig. 3 (not shown), is operated into engagement with a further control to connect into circuit a computor 60 which operates in the manner described in Specification 675,751. Specification 662,831 also is referred to.